A federal officer rubbed the cotton strip over his palms and fingers as Kerner waited in a security screening line at Tampa International Airport on Monday. In less than a minute, a device that looks like a computer printer swallowed the swab and reported his hands were free of any bomb residue.

"It didn't slow down the line and was fairly convenient,'' said the 31-year-old Las Vegas resident. "If it's good for security, I'm fine with it.''

The technology isn't new. But Transportation Security Administration officers now are patrolling airports with the portable devices to randomly check passengers and their carry-ons for traces of explosives. They'll mostly test travelers waiting at airport gates or in regular security screening lines.

"The TSA has many layers of security, and we're introducing another layer,'' said spokeswoman Sari Koshetz.

Soon after the attempted Christmas Day plot to bomb a U.S.-bound flight, the TSA tried the roaming tests at five airports, including Orlando International. Suspect Farouk Abdulmutallab passed through a metal detector in an Amsterdam airport, but metal detectors can't pick up the powdered explosives that officials say were sewn inside his underwear.

Last month, the TSA announced plans to roll out the roving bomb detectors nationwide. The program should be in all U.S. airports by next week.

Explosive trace detectors were an early tool for the fledgling TSA months after the 9/11 terrorist attacks. The early machines were bulky and anchored at airport security checkpoints. Newer models are the size of a briefcase. The TSA plans to spend $40 million next year for 800 new detectors, all highly sensitive to a wide range of chemicals.

At Tampa International, TSA officers roll the explosive detectors on carts or perch them on tables. Besides testing travelers at security lines and gates, they could randomly select people in any "sterile'' areas past security checkpoints, Koshetz said.

On its blog (tsa.gov/blog), the TSA acknowledges that people who are in contact with "accelerants and munitions'' — members of the military, firefighters, police and sport shooters — could set off alarms.

"No matter how much of an expert you are at traveling, it's not guaranteed that you won't be stopped for additional screening of some sort,'' says the blog. The agency says it has long-standing procedures to deal with bad guys while clearing those who aren't a threat.

TSA officials don't talk about what specific materials the detectors flag as dangerous. It's been reported that passengers who recently took nitroglycerin heart medicine can set off the detectors.

"Just be aware of what you've been doing before coming to the airport,'' Koshetz said.

Travelers flagged by the detectors must go through secondary screening, such as a pat-down search or scanning by a machine that can identify weapons beneath clothing. People who refuse the trace explosive test can be kept from flying.

Steve Huettel can be reached at huettel@sptimes.com or (813) 226-3384.